Oscilloscopic control device



Nov. 28, 1961 C. A. DEUTSCHLE OSCILLOSCOPIC CONTROL DEVICE Filed Aug. 2, 195'? f2/rari.

3,011,063 OSCILLOSCOPIC CONTROL DEVICE v Cecil A. Deutschle, Torrance, Calif., assignor to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Filed Aug. 2, 1957, Ser. No. 677,176 4 Claims. (Cl. 307-32) This invention relates to control means for cathode ray Oscilloscopes, and particularly to a device for controlling the position of the display thereon. n

The invention resides in the use of Wheatstones bridge circuit arrangement employing a solid sheet of flexible high resistance material, which may be distorted along two mutually perpendicular axes to vary the electrical resistance existing in the several branches of the bridge circuit. s

In the prior art, centering the display pattern has been accomplished by the use of means such as pivoted rods actuating two right-angle, rotary motion, mechanical resolvers. The resolvers, in turn, actuate devices to convert rotary motion to voltages, and the two quadrant voltages are used to locate the position of the pattern displayed on an oscilloscope. Included with this arrangement must be a mechanism for returning the control rods to their starting positions when the positioning forces are removed. It has been found extremely diiiicult to bring such rotary motion resolvers back to zero position. The output voltages are not smoothly variable because of the static friction and the inertia in the resolvers and the converters, while the static 'friction and the inertia of these moving parts require a relatively large actuating force. Devices of this type are comparatively slow acting, and a certain amount of back-lash and inaccuracy is inherent in their design. This basic ditiiculty exists even though many complicated components, manufactured to very close tolerances, are used. Their manufacture has been, as alresult, quite expensive.

In the present invention, these diiiiculties are resolved by replacing such costly and complicated mechanisms with a. simple device for introducing resistance smoothly variable in value along two mutually perpendicular axes by the manipulation of a single handle. The variable resistance is obtained by mounting a flat annular sheet of conductive rubber between an insulating ring and four quadrantally disposed conducting members in a suitable framework, which permits a control stick passing centrally through, and electrically connected to, the conductive rubber, to be moved as desired along two mutually perpendicular axes while being held pi'votally at one end by retaining means, including a ball and socket joint. The four quadrantally disposed plates are then connected in a circuit arrangement of the conventional Wheatstone bridge type with suitable externally disposed adjusting resistors and voltage sources. Movement of the controlvstick in any direction about its pivotally disposed lower end will cause deformation of the rubber sheet. The deformations result in variations in kthe electrical resistance of the conductive rubber. By suitable electrical connections, these variations are translated into voltage variations along the display axes. For example, the stick may be so moved that no movement will occur along the X axis while there will be compression along the Y axis perpendicular thereto on oneiside of the stick and an elongation along the same axis on the opposite side of the stick. This would cause a resistance change solely along the Y axis. This makes use of the resistance characteristic of conductive rubber. This material, well known in the art, consists of arubber carrier in which high resistance conductive material has been uniformly dispersed. As the conducting particles are brought closer together by compression, the resistance l rUnited States Patent() y 3,011,063 Patented Nov. 28, 1961 ice , value of the material is gradually reduced. If the materemoved from the control stick. This characteristic affords an obvious advantage over the use of wire-wound resistances for example, in which the variations must take place in discrete steps, however ine, and over mechanical resolvers, in which the return to zero position is obtained only with ditiiculty.

It will be apparent, therefore, that the primary object of the invention is to improve vmeans for controlling the position of the display on a cathode ray tube.

An additional object is to provide positioning means capable of infinitely tine variation inadjustment.

Another object is to simplify the mechanisms required for the control of cathode ray tube displays.

A further object is to simplify the return to zero position when no deilccting forces are present.

These and other objects will be apparent from consideration of the following description in connection with the drawings, in which:

FIG. l is a schematic side sectional view of a preferred embodiment of the invention taken in the plane indicated by line 1--1 of yFIG. 2;

FIG. 2 is a top view of a modiied embodiment of the invention.

FIG. 3y is a schematic circuit diagram showing the method of operation of the invention.

Referring now to ythe drawings' for a more detailed description of 'the invention, a side sectional view of a preferred embodiment is shown in FIG. 1, with a top view shown in FIG. 2. The control unit indicated generally as 1 includes a mounting kbase 2, from which extend upwardly supporting walls 4. An insulating plate 5 may be mounted by conventional means on top of walls 4, with a circular bore 6 formed centrally therethrough. The insulating Iplate 5 may be secured to the supporting ,walls 4 lby conventional means such as screws 7. p

Four quadrantal plates 9, 10, 11 and 12 are mounted on top of the insulating plate 5. Each of these quadrantal plates is made of a highly conductive material, such as brass, of suliicient rigidity to act as a firm support for a conductive rubber layer 14, which is mounted thereover and held securely thereagainst by a superposed insulating plate 15. The insulating plate 15 has formed therethrough a central bore 16 coaxial with the bore 6 formed through the insulating plate 5. y yThe quadrantal connecting plates 9, 10, 11 and 12 may have the `form' of squares from which a segment of a circle lhas been removed,y leaving the centrally disposed margins 17, 18, 19 and 20 as arcuate portions of a circle concentric with the bores 6 and 16 formed through the insulating plates 5 and 15, respectively.

Within the supporting walls 4 a mounting socket 21 is fixed to the base 2 with its center coaxial with bores 6 and 16. The receiving portion 22 of the socket 21 is spherical in curvature and forms the pivotal support for the control rod, indicated generally -as 23. Receiving portion 22 is adapted to receive a spherical ball 24,'having a threaded shank 25 fixed therein and extending vertically upward through an insulating connecting sleeve 26. Sleeve 26 also has iixed 'therein in axial alignment with a ball 24 and threaded shank 25, a conducting rod 27 to which a exible electrical lead 29 may be connected. Conducting rod 27 may terminate at its upper end in a reduced diameter threaded connecting portion 30, passing through the conductive rubber layer 14, and having lthreadably joined thereto a manipulating handle 31 of insulating material. The control rod 23 including the handle 31 is arranged to exert a firm grip on the conductive rubber layer 14 in a position coaxial lwith the ball `and socket joint, and introducing no stress laterally in the conductive rubber layer 14.

The quadrantal plates 9, 10, 11 and 12 are secured in position with their centrally disposed margins 17, 18, 19 and 20 coaxial about the control rod 23 by conventional means, such as screws 32, fastened in the insulating plate 5. The conductive rubber layer 14, in turn, is fixed in relation to the quadrantal plates 9, 10, 11 and l2, by means of mounting bolts 34, extending through the superposed insulating plate 15, supporting walls 4, quadrantal plates 9, lll, 11 and 12, and the insulating plate 5. The sandwich thus formed may be adjusted by means of bolts 34 to provide a uniform degree of compression throughout the entire conductive rubber layer 14.

It will be apparent that the resistance of that portion of the conductive rubber layer 14 disposed between the conducting Vrod 27 and the margin 17 of the quadrantal plate 9 will be reduced as the rod is moved in that direction. At the same time, the resistance between the rod andthe margin 18 of the opposite quadrantal plate 10, will be correspondingly increased. As long as the motion continues exactly in this direction, which we may call the X axis, there will be no change in the resistance along a Y axis normal thereto, between the quadrantal plates 11 andf12. Movement along such a Y axis may, of course, be performed independently of that along the X axis, although in normal operation the movement will probably take place more frequently in directions having discrete components along both X and Y axes, so that variations will be introduced in more than one arm of the bridge. Variations will be introduced in all of the bridge arms, producing detiections of the beam along both X and Y axes to restore it to zero position.

The circuit as shown schematically in FIG. 3, illustrates how the device may be used with a potential source 40 supplying` a flow of current through the bridge portions including Ithe quadrantal connection plates 9 and lll, the rubber layer 14 and the control rod portion 27, to the X control leads 41 and 42, through outside bridge arm 44 and outside adjustable bridge arm 4S.

Similarly, potential source 50 supplies current through the bridge portions including quadrantal connection plates 11 and 12, rubber layer 14 and control rod portion 27 to the Y control leads 51 and 52, an outside bridge `arm 54 and outside adjustable bridge arm 55.

The output X leads 41 and 42 and output Y leads 51 yand 52 furnish the output quadrature voltages for the oscilloscope deiiection. If the control rod 27 s grounded, not shown, the outputs would be push-pull in nature. If two single-ended signals are desired, one of each of the output signal pairs should be grounded. These connections are conventional.

With the arrangement as shown in FIG. 1, wherein the conducting paths from the control stick 23 to the quadrantal plates are all equal, ya 1:1 correspondence will be obtained in X and Y deiiections. It is possible to vary the comparative etfects, however, along the two Iaxes by making these distances unequal in accordance with some desired function. For example, the margin of the quadrantal plates presented to the control stick might be oval, elliptical, or of some other geometrical configuration in order to secure a different relation between the X and Y correcting resistance values.

A second order fringe eiect may be found if the pressures exerted on all the quadrant plates are not uniformly adjusted. To minimize this possibility, an alternative embodiment 60 is shown in FIG. 2 in that portion relating to the shape of the conductive rubber layer. In this embodiment 60, a conductive rubber layer 61 is provided that includes four sectorial portions 62, 63, 64 and 65. When these rubber portions are in place, their periphery will have a circular shape rather than the square shape shown in FIG. l. With this alternative form, the quadrant plates are made to exert radial pressure on the outer edges of the conducting rubber. It may then be desirable to use two separate rubber layers, not shown, for the bridge portions controlling the X and Y adjustments.

Obviously, other materials than conductive rubber may be used, providing they `are such as to respond by substantial resistance variations to changes in pressure applied thereto, and are sufficiently elastic to permit relatively wide movement and yet return to their original configuration when the pressure is relieved.

It is also possible to make the electrical connections to this high resistance conducting material by means other than compression of the top plate thereon relative to the quadrant plates and of the separate parts of control stick 23 against the rubber sheet. For example, electrical connections m-ay be molded into the conductive rubber with a hard-setting rubber cement.

The invention as described thus provides a simple and easily constructed Iarrangement for securing at low cost a self-centering device adjustable smoothly over the entire range desired, with no complicated and expensive components.

What is claimed is:

l. A transducer having 'a member comprising a sheet of mechanically deformable material having an electrical resistance that varies with deformations of said material, a iirst current source electrically connected to diametrically opposite portions of said member for supplying currents of the same polarities thereto, a second current source electrically connected to a secondy pair of di-ametrically opposite portions of said member for supplying currents of the same polarities thereto, means permanently connected to a central point on said member to form a fixed contact therebetween so said currents may ow between said portions and said means, said point being positioned so that the resistances between said portions and said central point will normally be substantially equal whereby said currents will be balanced, .and means connected to said member for mechanically deforming said member whereby the resistances between said portions and said central point will vary and cause said currents to vary. b

2. A transducer for providing ya plurality of electrical signals indicative of the mechanical position of a rnember, said transducer comprising support means, a sheet of mechanicallyA deformable material mounted on said support means, said material having an electrical resistance that varies with deformations thereof, said sheet including a tirst pair of diametrically opposite peripheral portions adapted to be connected to a first current source for receiving currents of the same polarities therefrom, said sheet also including a second pair of diametrically opposite peripheral portions that are conjugately disposed to said irst pair of peripheral portions and are adapted to be connected to a second current source for receiving currents of the same polarities therefrom, means permanently connected to a central point on said sheet to form a permanent electrical contact therebetween, said central point being positioned so that the electrical resistances between said point and said peripheral portions will normally be substantially equal whereby said currents will normally be balanced, and means mechanically interconnected with said sheet whereby movement of said member will cause the resistances between said portions and said central point to Vary and cause said currents at said peripheral portions to vary in proportion to said movements.

3. In a control unit for a cathode ray oscilloscope the combination of support means, an elastic sheet of rel-atively high resistance electrical conducting material mounted on said support means, first circuit means connected to diametrically opposite Isides of said sheet for supplying electrical currents thereto of similar polarity, second circuit meaus connected to diametrically opposite sides of said sheet and conjugate to said sides so as to form la resistive bridge circuit, said first circuit means including resistive loads for producing voltages indicative of said iirst currents, said second circuit means including separate resistive loads for developing voltages indicative of said second currents, means permanently connected to a center point on said sheet to for-m a ixed electrical contact, said point being positioned so that the resistances between said point and said terminals will 'be substantially identical whereby said bridge will be balanced, and means for mechanically deforming said sheet for changing said resistances so that said bridge will become unbalanced and said volt-ages will vary `in proportion to the amount of movement of said means.

4. In a control unit providing control signals for positioning the electron beam in a cathode ray oscilloscope, said control unit comprising suppor't means, -a sheet of elastic conductive rubber mounted on said support means,

a first current source operatively interconnected with dametrically opposite portions of said sheet by means of separate resistive loads for ysupplying currents of the same polarity thereto, a second current source electrically in terconnected with dametrically opposite portions of said sheet by a second set of resistive'loads, means permanently connected to the center of said sheet to form a fixed electrical contact and thereby form a bridge circuit which is normally balanced, andmeans pivotally mounted on said support and mechanically connected to the center of said sheet whereby movement thereof will deform said sheet and provide voltages across said resistive loads indicative of the amount of movement of said member.

References Cited in the file of this patent UNITED STATES PATENTS 2,236,222 Smyth Mar. 25, 1941 2,471,601 Albright Mar. 3l, 1949 .2,694,128y Maurin Nov. 9, 1954 2,762,234 Dodd Sept. 11, 1956 

